We continue to develop the utility of mass spectrometry (MS) for facilitating atomic resolution studies of proteins by x-ray diffraction and NMR spectroscopy. We have found that MS is enormously useful at every stage of these studies, including:. 1) Determining the purity and fidelity of the recombinant protein constructs . 2) Elucidating tightly folded structural domains to assist in the design of optimal protein constructs. 3) Assessing heavy atom incorporation 4) Assessing the stochiometry of multiple components in co-crystals. Progress continues to be steady and we are getting ready to prepare another manuscript describing our newer methologies (which will be of considerable use to structural biologists).